1. Field of the Invention
This invention relates to the field of oilfield equipment, and in particular to a system and method for the conversion of a conventional annular blow-out preventer (BOP) between an open and non-pressurized mud-return system and a closed and pressurized mud-return system for managed pressure drilling or underbalanced drilling.
2. Description of the Related Art
Marine risers extending from a well head on the floor of the ocean have traditionally been used to circulate drilling fluid back to a drilling structure or rig through the annular space between the drill string and the internal diameter of the riser. The riser must be large enough in internal diameter to accommodate the largest drill string that will be used in drilling a borehole. For example, risers with internal diameters of 19½ inches (49.5 cm) have been used, although other diameters can be used. An example of a marine riser and some of the associated drilling components, such as shown herein in FIGS. 1 and 2, is proposed in U.S. Pat. No. 4,626,135.
The marine riser is not generally used as a pressurized containment vessel during conventional drilling operations. Pressures contained by the riser are generally hydrostatic pressure generated by the density of the drilling fluid or mud held in the riser and pressure developed by pumping of the fluid to the borehole. However, some remaining undeveloped reservoirs are considered economically undrillable using conventional drilling operations. In fact, studies sponsored by the U.S. Department of the Interior, Minerals Management Service and the American Petroleum Institute have concluded that between 25% and 33% of all remaining undeveloped reservoirs are not drillable using conventional overbalanced drilling methods, caused in large part by the increased likelihood of well control problems such as differential sticking, lost circulation, kicks, and blowouts.
Drilling hazards such as gas and abnormally pressured aquifers relatively shallow to the mud line present challenges when drilling the top section of many prospects in both shallow and deep water. Shallow gas hazards may be sweet or sour and, if encountered, reach the rig floor rapidly. Blowouts at the surface have occurred due to lack of time to close the rigs BOP. If sour, even trace amounts of such escaping gasses create health, safety and environmental (HSE) hazards, as they are harmful to humans and detrimental to the environment. There are U.S. and Canadian regulatory restrictions on the maximum amount of exposure workers can have to such gases. For example, the Occupational Safety and Health Administration (OSHA) sets an eight-hour daily limit for a worker's exposure to trace amounts of H2S gas when not wearing a gas mask.
Pore pressure depletion, narrow drilling windows due to tight margins between formation pressure and fracture pressure of the open hole, growing requirement to drill in deeper water, and increased drilling costs indicate that the amount of known reservoirs considered economically un-drillable with conventional drilling operations will continue to increase. New and improved techniques, such as managed pressure drilling and underbalanced drilling, have been used successfully throughout the world in certain offshore drilling environments. Managed pressure drilling has recently been approved in the Gulf of Mexico by the U.S. Department of Interior, Minerals Management Service, Gulf of Mexico Region. Managed pressure drilling is an adaptive drilling process that does not invite hydrocarbons to the surface during drilling. Its primary purpose is to more precisely manage the wellbore pressure profile while keeping the equivalent mud weight above the formation pressure at all times, whether circulating or shut in to make jointed pipe connections. To stay within the drilling window to a deeper depth with the mud in the hole at the time, for example to drill a deeper open hole perhaps to eliminate need for another casing string, the objective may be to drill safely at balance, nearer balanced, or by applying surface backpressure to achieve a higher equivalent mud weight (EMW) than the hydrostatic head of the drilling fluid. Underbalanced drilling is drilling with the hydrostatic head of the drilling fluid and the equivalent mud weight when circulating designed to be lower than the pressure of the formations being drilled. The hydrostatic head of the fluid may naturally be less than the formation pressure, or it can be induced.
These new and improved techniques present a need for pressure management devices, such as rotating control heads or devices (referred to as RCDs) and rotating marine diverters. RCDs, similar to the one disclosed in U.S. Pat. No. 5,662,181, have provided a dependable seal between a rotating tubular and the marine riser for purposes of controlling the pressure or fluid flow to the surface while drilling operations are conducted. Typically, an inner portion or member of the RCD is designed to seal around a rotating tubular and rotate with the tubular using internal sealing element(s) and bearings. Additionally, the inner portion of the RCD allows the tubular to move axially and slidably through the RCD. The term “tubular” as used herein means all forms of drill pipe, tubing, casing, drill collars, liners, and other tubulars for oilfield operations as are understood in the art.
U.S. Pat. No. 6,913,092 B2 proposes a seal housing comprising a RCD positioned above sea level on the upper section of a marine riser to facilitate a closed and mechanically controlled pressurized system that is useful in underbalanced subsea drilling. An internal running tool is proposed for positioning the RCD seal housing onto the riser and facilitating its attachment thereto. A remote controlled external disconnect/connect clamp is proposed for hydraulically clamping the bearing and seal assembly of the RCD to the seal housing.
It has also been known to use a dual density fluid system to control formations exposed in the open borehole. See Feasibility Study of a Dual Density Mud System For Deepwater Drilling Operations by Clovis A. Lopes and Adam T. Bourgoyne, Jr., ©1997 Offshore Technology Conference. As a high density mud is circulated to the rig, gas is proposed in the 1997 paper to be injected into the mud column in the riser at or near the ocean floor to lower the mud density. However, hydrostatic control of formation pressure is proposed to be maintained by a weighted mud system, that is not gas-cut, below the seafloor.
U.S. Pat. No. 6,470,975 B1 proposes positioning an internal housing member connected to a RCD below sea level with a marine riser using an annular blowout preventer (“BOP”) having a marine diverter, an example of which is shown in the above discussed U.S. Pat. No. 4,626,135. The internal housing member is proposed to be held at the desired position by closing the annular seal of the BOP so that a seal is provided between the internal housing member and the inside diameter of the riser. The RCD can be used for underbalanced drilling, a dual density fluid system, or any other drilling technique that requires pressure containment. The internal housing member is proposed to be run down the riser by a standard drill collar or stabilizer.
U.S. Pat. No. 7,159,669 B2 proposes that the RCD held by an internal housing member be self-lubricating. The RCD proposed is similar to the Weatherford-Williams Model 7875 RCD available from Weatherford International, Inc. of Houston, Tex.
U.S. Pat. No. 6,138,774 proposes a pressure housing assembly containing a RCD and an adjustable constant pressure regulator positioned at the sea floor over the well head for drilling at least the initial portion of the well with only sea water, and without a marine riser.
Pub. No. US 2006/0108119 A1 proposes a remotely actuated hydraulic piston latching assembly for latching and sealing a RCD with the upper section of a marine riser or a bell nipple positioned on the riser. As best shown in FIG. 2 of the '119 publication, a single latching assembly is proposed in which the latch assembly is fixedly attached to the riser or bell nipple to latch an RCD with the riser. As best shown in FIG. 3 of the '119 publication, a dual latching assembly is also proposed in which the latch assembly itself is latchable to the riser or bell nipple, using a hydraulic piston mechanism.
Pub. No. US 2006/0144622 A1 proposes a system for cooling the radial seals and bearings of a RCD. As best shown in FIG. 2A of the '622 publication, hydraulic fluid is proposed to both lubricate a plurality of bearings and to energize an annular bladder to provide an active seal that expands radially inward to seal around a tubular, such as a drill string.
Marine BOP diverters are used in conventional hydrostatic pressure drilling on drilling rigs or structures. Manufacturers of marine BOP diverters include Hydril Company, Vetco Gray, Inc., Cameron, Inc., and Dril-Quip, Inc., all of Houston, Tex. When the BOP diverter's seals are closed upon the drill string, fluid is safely diverted away from the rig floor. However, drilling operations must cease because movement of the drill string will damage or destroy the non-rotating annular seals. During normal operations the diverter's seals are open. There are a number of offshore drilling circumstances, not related to well control, where it would be advantageous to rotate and move the drill string within a marine diverter with closed seals. Two examples are: 1) slow rotation to prevent the drill string from sticking when circulating out riser gas, which in deep wells can take many hours, and 2) lifting the drill string off the bottom to minimize annulus friction pressure after circulating out riser gas and before resuming drilling operations. Being able to drill with a closed seal would also allow drilling ahead with a managed back-pressure applied to the annulus while maintaining a more precise well bore pressure profile.
A marine diverter converter housing for positioning with an RCD, as shown in FIG. 3, has been used in the recent past. However, the housing must match the inside profile of one of the many makes and models of BOP marine diverters, some of which are disclosed above, in which it is used. Moreover, the annular elastomer packer seal and hydraulic actuated piston therein must be removed before the converter housing is positioned therein.
The above discussed U.S. Pat. Nos. 4,626,135; 5,662,181; 6,138,774; 6,470,975 B1; 6,913,092 B2; and 7,159,669 B2; and Pub. Nos. U.S. 2006/0108119 A1 and U.S. 2006/0144622 A1 are incorporated herein by reference for all purposes in their entirety. With the exception of the '135 patent, all of the above referenced patents and patent publications have been assigned to the assignee of the present invention. The '135 patent is assigned on its face to the Hydril Company of Houston, Tex.
While drilling rigs are usually equipped with an annular BOP marine diverter used in conventional hydrostatic pressure drilling, a need exists for a system and method to efficiently and safely convert the annular BOP marine diverters between conventional drilling and managed pressure drilling or underbalanced drilling. The system and method would allow for the conversion between a conventional annular BOP marine diverter and a rotating marine diverter. It would be desirable for the system and method to require minimal human intervention, particularly in the moon pool area of the rig, and to provide an efficient and safe method for positioning and removing the equipment. It would further be desirable for the system to be compatible with a variety of different types and sizes of RCDs and annular BOP marine diverters.